Tài liệu Nickel and ITS Alloys ppt

Nickel Alloys The corrosion resistance of nickel makes it particularly useful for maintaining product purity in the handling of foods, synthetic fibers, and caustic alkalies, and also in

5.1 INTRODUCTION

Nickel, the 24th element in abundance, has an average content of 0.016% in the outer 10 miles of the earth's crust This is greater than the total for copper, zinc, and lead However, few of these deposits scattered throughout the world are of commercial importance Oxide ores commonly called laterites are largely distributed in the tropics The igneous rocks contain high magnesium contents and have been concentrated by weathering Of the total known ore deposits, more than 80% is contained in laterite ores The sulfide ores found in the northern hemispheres do not easily concentrate

by weathering The sulfide ores in the Sudbury district of Ontario, which contain important by-products such as copper, cobalt, iron, and precious metals are the world's greatest single source of nickel.1

Nickel has an atomic number of 28 and is one of the transition elements in the fourth series in the periodic table The atomic weight is 58.71 and density is 8.902 g/cm3 Useful properties of the element are the modulus of elasticity and its magnetic and magnetostrictive properties, and high thermal and electrical conductivity Hydrogen is readily adsorbed on the surface of nickel Nickel will also adsorb other gases such as carbon monoxide, carbon dioxide, and ethylene It is this ca-pability of surface adsorption of certain gases without forming stable compounds that makes nickel

an important catalyst.2

As an alloying element, nickel is used in hardenable steels, stainless steels, special corrosion-resistant and high-temperature alloys, copper-nickel, "nickel-silvers," and aluminum-nickel Nickel imparts ductility and toughness to cast iron

Approximately 10% of the total annual production of nickel is consumed by electroplating pro-cesses Nickel can be electrodeposited to develop mechanical properties of the same order as wrought nickel; however, special plating baths are available that will yield nickel deposits possessing a hard-ness as high as 450 Vickers (425 BHN) The most extensive use of nickel plate is for corrosion protection of iron and steel parts and zinc-base die castings used in the automotive field For these applications, a layer of nickel, 0.0015-0.003 in thick, is used This nickel plate is then finished or covered with a chromium plate consisting in thickness of about 1% of the underlying nickel plate thickness in order to maintain a brilliant, tarnish-free, hard exterior surface

Mechanical Engineers' Handbook, 2nd ed., Edited by Myer Kutz.

ISBN 0-471-13007-9 © 1998 John Wiley & Sons, Inc

CHAPTER 5

NICKEL AND ITS ALLOYS

T H Bassford

Jim Hosier

Inco Alloys International, Inc.

Huntington, West Virginia

5.1 INTRODUCTION 71

5.2 NICKELALLOYS 72

5.2.1 Classification of Alloys 72

5.2.2 Discussion and Applications 72

5.3 CORROSION 80

5.4 FABRICATION 82

5.4.1 Resistance to Deformation 82

5.4.2 Strain Hardening 82

5.5 HEATTREATMENT 84 5.5.1 Reducing Atmosphere 84 5.5.2 Prepared Atmosphere 85 5.6 WELDING 86 5.7 MACHINING 86 5.8 CLOSURE 88

5.2 NICKELALLOYS

Most of the alloys listed and discussed are in commercial production However, producers from time

to time introduce improved modifications that make previous alloys obsolete For this reason, or economic reasons, they may remove certain alloys from their commercial product line Some of these alloys have been included to show how a particular composition compares with the strength or corrosion resistance of currently produced commercial alloys

5.2.1 Classification of Alloys

Nickel and its alloys can be classified into the following groups on the basis of chemical composition.3

Nickel

(1) Pure nickel, electrolytic (99.56% Ni), carbonyl nickel powder and pellet (99.95% Ni); (2) com-mercially pure wrought nickel (99.6-99.97% nickel); and (3) anodes (99.3% Ni)

Nickel and Copper

(1) Low-nickel alloys (2-13% Ni); (2) cupronickels (10-30% Ni); (3) coinage alloy (25% Ni); (4) electrical resistance alloy (45% Ni); (5) nonmagnetic alloys (up to 60% Ni); and (6) high-nickel alloys, Monel (over 50% Ni)

Nickel and Iron

Wrought alloy steels (0.5-9% Ni); (2) cast alloy steels (0.5-9% Ni); (3) alloy cast irons (1-6 and 14-36% Ni); (4) magnetic alloys (20-90% Ni): (a) controlled coefficient of expansion (COE) alloys (29.5-32.5% Ni) and (b) high-permeability alloys (49-80% Ni); (5) nonmagnetic alloys (10-20% Ni); (6) clad steels (5-40% Ni); (7) thermal expansion alloys: (a) low expansion (36-50% Ni) and (b) selected expansion (22-50% Ni)

Iron, Nickel, and Chromium

(1) Heat-resisting alloys (40-85% Ni); (2) electrical resistance alloys (35-60% Ni); (3) iron-base superalloys (9-26% Ni); (4) stainless steels (2-25% Ni); (5) valve steels (2-13% Ni); (6) iron-base superalloys (0.2-9% Ni); (7) maraging steels (18% Ni)

Nickel, Chromium, Molybdenum, and Iron

(1) Nickel-base solution-strengthened alloys (40-70% Ni); (2) nickel-base precipitation-strengthened alloys (40-80% Ni)

Powder-Metallurgy Alloys

(1) Nickel-base dispersion strengthened (78-98% Ni); (2) nickel-base mechanically alloyed oxide-dispersion-strengthened (ODS) alloys (69-80% Ni)

The nominal chemical composition of nickel-base alloys is given in Table 5.1 This table does not include alloys with less than 30% Ni, cast alloys, or welding products For these and those alloys

not listed, the chemical composition and applicable specifications can be found in the Unified Num-bering System for Metals and Alloys, published by the Society of Automotive Engineers, Inc.

5.2.2 Discussion and Applications

The same grouping of alloys used in Tables 5.1, 5.2, and 5.3, which give chemical composition and mechanical properties, will be used for discussion of the various attributes and uses of the alloys as

a group Many of the alloy designations are registered trademarks of producer companies

Nickel Alloys

The corrosion resistance of nickel makes it particularly useful for maintaining product purity in the handling of foods, synthetic fibers, and caustic alkalies, and also in structural applications where resistance to corrosion is a prime consideration It is a general-purpose material used when the special properties of the other nickel alloys are not required Other useful features of the alloy are its magnetic and magnetostrictive properties; high thermal and electrical conductivity; low gas content; and low vapor pressure.4

Typical nickel 200 applications are food-processing equipment, chemical shipping drums,

electri-cal and electronic parts, aerospace and missile components, caustic handling equipment and piping, and transducers

Nickel 201 is preferred to nickel 200 for applications involving exposure to temperatures above

3160C (60O0F) Nickel 201 is used as coinage, plater bars, and combustion boats in addition to some

of the applications for Nickel 200

Permanickel alloy 300 by virtue of the magnesium content is age-hardenable But, because of its

low alloy content, alloy 300 retains many of the characteristics of nickel Typical applications are

Other Elements C

Si Mn

Nb Ti

Al Mo

Cr Fe

Cu Ni

Material

0.38 Mg

0.04 S

4.0Co 20Co

14Co

14 Co

0.07 0.01 0.29 0.16 0.12 0.07 0.15 0.17 0.08 0.05 0.01 0.03 0.04 0.04 0.05 0.07 0.01 0.03 0.05 0.03 0.03 0.03 0.03 0.02 0.02

0.03 0.03 0.04 0.50 0.10 0.04 0.17 0.12 0.25 0.25 0.18 0.25 0.50 0.50 0.25 0.22 0.10 1.0 0.09 0.06 0.50 0.17 0.08

0.23 0.23 0.11 0.25 1.0 0.01 1.0 0.70 0.5 0.5 0.18 0.18 0.50 0.75 0.75 0.50 0.60 0.25 0.8 0.5 0.5 0.40 0.09 0.05

3 5.1 1

2.9 4.70

0.49 0.44

0.48

1.8 0.9 2.5 0.38 0.38 0.90 2.10 3.0 2.6

2.6 1.40

4.44

0.1 2.94

1.35 0.20 0.5 0.70 0.38 0.38 0.10 0.35 1.0 0.2

0.55 0.90 1.5

3.0

3 3 6 3.2

15.5 23.0 30 16 19 15.5 20 20 22.5 21 13 18

5.33

0.02 0.08 1.00 0.03 1.25 0.64 8.0 14.1 9.0 40 18.5 7 46 46 30 28 BaI BaI 61.5 57.4 48.5 41.5 41.9

32 45.3 31.6 30 0.25 0.50 0.15 0.15 0.25 0.38 0.38 1.75 1.8

0.05 0.10

99.6 99.7 98.7 94.3 65.4 54.6 65.3 65.0 76 60.5 60 41.5 53.5 73 31 31 42 43.2 44 38 36 41.6 42.3 38 37.6

Nickel

Nickel 200

Nickel 201

Permanickel alloy 300

Duranickel alloy 301

Nickel-Copper

Monel alloy 400

Monel alloy 404

Monel alloy R-405

Monel alloy K-500

Nickel-Chromium-Iron

Inconel alloy 600

Inconel alloy 601

Inconel alloy 690

Inconel alloy 706

Inconel alloy 718

Inconel alloy X-750

Nickel-Iron-Chromium

Incoloy alloy 800

Incoloy alloy 80OH

Incoloy alloy 825

Incoloy alloy 925

Pyromet 860

Refractaloy 26

Nickel— Iron

NiIo alloy 36

NiIo alloy 42

Ni-Span-C alloy 902

Incoloy alloy 903

Incoloy alloy 907

Table 5.1 Nonimal Chemical Composition (wt%)

Other Elements C

Si Mn

Ti Nb Al

Mo Cr

Fe Material Ni Cu

<1 W, <2.5 Co 2.5 Co, 4 W, 0.35 V

<2Co 12.5 Co

10 Co, 0.005 B

11 Co <0.010B

8 Co, 3.5 W, 0.01 B, 0.05 Zr 15Co

18 Co 0.007 B

12 Co 1 W, 0.005 B

16 Co 0.02 B 18.5 Co, 0.025 B 7.2 Co, 8.4 W, 0.008 B, 0.06 Zr

14 Co, 0.006 B, 0.05 Zr 2ThO2 1.7 ThO2 0.6 Y2O3

4 W, 2 Ta, 1.1 Y2O3

0.10

<0.05

<0.01

<0.01 0.07 0.03 0.15 0.09 0.15 0.06 0.08 0.05 0.04 0.07 0.24 0.08

0.05 0.05

1.5

<1

<1

<0.5

0.05

<1

<0.08

<0.08

<0.5

0.1

2.1

3.6 3.5

<0.7

<0.4 2.6 3.1 2.5 3.5 3.0 3.0 2.9 3.5 3.2

3

0.5 2.5

1

<0.4 1 1.5 3.5 4.4 3.0 2.0 4.2 4.4 1.9

1.5

0.3 4.5

9 6.5 16 15.5 9 9 10 10 3.5 5.3 4 6 4 5.0 1.6

4.3

2

22 22 15.5 16 22 21.5 19 19 14 15 19 19 17 15 16.3

19

20 20 15

19 19.5 5.5

<3 2.5

<0.5

<4 9.5

<2

1.0

Nickel— Chromium— Molybdenum

Hastelloy alloy X BaP —

Hastelloy alloy G BaI 2

Hastelloy alloy C-276 BaI —

Hastelloy alloy C BaI —

Inconel alloy 617 54 —

Inconel alloy 625 BaI —

MAR-M-252 BaI —

Rene' 41 BaI —

Rene' 95 BaI —

Astroloy BaI —

Udimet 500 BaI —

Udimet 520 BaI —

Udimet 600 BaI —

Udimet 700 BaI —

Udimet 1753 BaI —

Waspaloy BaI <0.1

Nickel-Powder Alloys (Dispersion Strengthened)

TD-nickel 98 —

TD-NiCr BaI —

Nickel-Powder Alloys (Mechanically Alloyed)

Inconel alloy MA 754 78 —

Inconel alloy 69 —

MA 6000

Minimum Maximum Balance

Table 5.1 (Continued)

Table 5.2 Mechanical Properties of Nickel Alloys

Material

Nickel

Nickel 200

Nickel 201

Permanickel alloy 300

Duranickel alloy 301

Nickel-Copper

Monel alloy 400

Monel alloy 404

Monel alloy R-405

Monel alloy K-500

Nickel— Ch romium—Iron

Inconel alloy 600

Inconel alloy 601

Inconel alloy 690

Inconel alloy 706

Inconel alloy 718

Inconel alloy X-750

Nickel-Iron-Chromium

Incoloy alloy 800

Incoloy alloy 80OH

Incoloy alloy 825

Incoloy alloy 925

Pyromet 860

Refractaloy 26

Nickel— Iron

NiIo alloy 42

Ni-Span-C alloy 902

Incoloy alloy 903

Incoloy alloy 907

Nickel-Chromium-Molybdenum

Hastelloy alloy X

Hastelloy alloy G

Hastelloy alloy C-276

Inconel alloy 617

Inconel alloy 625

MAR-M-252

Rene' 41

Rene' 95

Astroloy

Udimet 500

Udimet 520

Udimet 600

Udimet 700

Udimet 1753

Waspaloy

0.2%

Yield Strength (ksi)a 21.5 15 38 132 31 31 56 111 50 35 53 158 168 102 48 29 44 119 115 100 37 137 174 163 52 56 51 43 63 122 120 190 152 122 125 132 140 130 115

Nickel-Powder Alloys (Dispersion Strengthened}

TD-Nickel

TD-NiCr

45 89

Nickel-Powder Alloys (Mechanically Alloyed)

Inconel alloy MA 754

Inconel alloy MA 6000

a MPa - ksi X 6.895

85 187

Tensile Strength (ksi)a 67 58.5 95 185 79 69 91 160 112 102 106 193 205 174 88 81 97 176 180 170 72 150 198 195 114 103 109 107 140 180 160 235 205 190 190 190 204 194 185 65 137 140 189

Elongation (%)

47 50 30 28 52 40 35 24 41 49 41 21 20 25 43 52 53 24 21 18 43 12 14 15 43 48.3 65 70 51 16 18 15 16 32 21 13 17 20 25 15 20 21 3.5

Rockwell Hardness 55Rb 45Rb 79Rb 36Rc

73 Rb 68Rb 86Rb 25Rc 90Rb

81 Rb 97Rb 40Rc 46Rc 33Rc 84Rb 72Rb 84Rb 34Rc

37 Rc

80Rb 33Rc 39Rc 42Rc

86Rb

81 Rb 96Rb

39Rc

—

grid lateral winding wires, magnetostriction devices, thermostat contact arms, solid-state capacitors, grid side rods, diaphragms, springs, clips, and fuel cells

Duranickel alloy 301 is another age-hardenable high nickel alloy, but is made heat treatable by

aluminum and titanium additions The important features of alloy 301 are high strength and hardness, good corrosion resistance, and good spring properties up to 3160C (60O0F); and it is on these me-chanical considerations that selection of the alloy is usually based Typical applications are extrusion press parts, molds used in the glass industry, clips, diaphragms, and springs

Nickel-Copper Alloys

Nickel-copper alloys are characterized by high strength, weldability, excellent corrosion resistance, and toughness over a wide temperature range They have excellent service in seawater or brackish water under high-velocity conditions, as in propellers, propeller shafts, pump shafts, and impellers and condenser tubes, where resistance to the effects of cavitation and erosion are important Corrosion rates in strongly agitated and aerated seawater usually do not exceed 1 mil/year

Monel alloy 400 has low corrosion rates in chlorinated solvents, glass-etching agents, sulfuric

and many other acids, and practically all alkalies, and it is resistant to stress-corrosion cracking Alloy

400 is useful up to 5380C (100O0F) in oxidizing atmospheres, and even higher temperatures may be used if the environment is reducing Springs of this material are used in corrosive environments up

to 2320C (45O0F) Typical applications are valves and pumps; pump and propeller shafts; marine fixtures and fasteners; electrical and electronic components; chemical processing equipment; gasoline and freshwater tanks; crude petroleum stills, process vessels, and piping; boiler feedwater heaters and other heat exchangers; and deaerating heaters

Monel alloy 404 is characterized by low magnetic permeability and excellent brazing

character-istics Residual elements are controlled at low levels to provide a clean, wettable surface even after prolonged firing in wet hydrogen Alloy 404 has a low Curie temperature and its magnetic properties

Table 5.3 1000-hr Rupture Stress (ksi)

Nickel-Chromium-Iron

Inconel alloy 600

Inconel alloy 601

Inconel alloy 690

Inconel alloy 706

Inconel alloy 718

Inconel alloy X-750

Nickel— Iron— Chromium

Incoloy alloy 800

Incoloy alloy 80OH

Incoloy alloy 825

Pyromet 860

Refractaloy 26

Nickel-Chromium-Moloybdenum

Hastelloy alloy X

Inconel alloy 617

Inconel alloy 625

MAR-M-252

Rene' 41

Rene' 95

Astroloy

Udimet 500

Udimet 520

Udimet 600

Udimet 700

Udimet 1753

Waspaloy

120O0F

14.5 28 16 85 85 68 20 23 26 81 65 31 52 60 79 102 125 112 110 85 102 98 89

Nickel-Powder Alloys (Dispersion Strengthened)

TD-Nickel

TD-NiCr

21

Nickel-Powder Alloys (Mechanically Alloyed)

Inconel alloy MA 754

Inconel alloy MA 6000

a MPa ksi x 6.895

38

150O0F

3.7 6.2

17

6.8 6.0 17 15.5 9.5 14 7.5 22.5 29 42 30 33 37 43 34 26 15

—

180O0F

1.5 2.2

1.9 1.3

3.8

8

7.5 6.5

10 8 19 22

200O0F

1.0

0.9

1.5

7 5 14 15

are not appreciably affected by processing or fabrication This magnetic stability makes alloy 404 particularly suitable for electronic applications Much of the strength of alloy 404 is retained at outgassing temperatures Thermal expansion of alloy 404 is sufficiently close to that of many other alloys as to permit the firing of composite metal tubes with negligible distortion Typical applications are waveguides, metal-to-ceramic seals, transistor capsules, and power tubes

Monel alloy R-405 is a free-machining material intended almost exclusively for use as stock for

automatic screw machines It is similar to alloy 400 except that a controlled amount of sulfur is added for improved machining characteristics The corrosion resistance of alloy R-405 is essentially the same as that of alloy 400, but the range of mechanical properties differs slightly Typical appli-cations are water meter parts, screw machine products, fasteners for nuclear appliappli-cations, and valve seat inserts

Monel alloy K-500 is an age-hardenable alloy that combines the excellent corrosion resistance

characteristics of the Monel nickel-copper alloys with the added advantage of increased strength and hardness Age hardening increases its strength and hardness Still better properties are achieved when the alloy is cold-worked prior to the aging treatment Alloy K-500 has good mechanical properties over a wide temperature range Strength is maintained up to about 6490C (120O0F), and the alloy is strong, tough, and ductile at temperatures as low as -2530C (-4230F) It also has low permeability and is nonmagnetic to -1340C (-21O0F) Alloy K-500 has low corrosion rates in a wide variety of environments Typical applications are pump shafts and impellers, doctor blades and scrapers, oil-well drill collars and instruments, electronic components, and springs

Nickel-Chromium-Iron Alloys

This family of alloys was developed for high-temperature oxidizing environments These alloys typ-ically contain 50-80% nickel, which permits the addition of other alloying elements to improve strength and corrosion resistance while maintaining toughness

Inconel alloy 600 is a standard engineering material for use in severely corrosive environments

at elevated temperatures It is resistant to oxidation at temperatures up to 11770C (215O0F) In addition

to corrosion and oxidation resistance, alloy 600 presents a desirable combination of high strength and workability, and is hardened and strengthened by cold-working This alloy maintains strength, ductility, and toughness at cryogenic as well as elevated temperatures Because of its resistance to chloride-ion stress-corrosion cracking and corrosion by high-purity water, it is used in nuclear re-actors For this service, the alloy is produced to exacting specifications and is designated Inconel alloy 60OT Typical applications are furnace muffles, electronic components, heat-exchanger tubing, chemical- and food-processing equipment, carburizing baskets, fixtures and rotors, reactor control rods, nuclear reactor components, primary heat-exchanger tubing, springs, and primary water piping Alloy 600, being one of the early high-temperature, corrosion-resistant alloys, can be thought of as being the basis of many of our present day special-purpose high-nickel alloys, as illustrated in Fig 5.1

Inconel alloy 601 has shown very low rates of oxidation and scaling at temperatures as high as

10930C (200O0F) The high chromium content (nominally 23%) gives alloy 601 resistance to oxidiz-ing, carburizoxidiz-ing, and sulfur-containing environments Oxidation resistance is further enhanced by the aluminum content Typical applications are heat-treating baskets and fixtures, radiant furnace tubes, strand-annealing tubes, thermocouple protection tubes, and furnace muffles and retorts

Inconel alloy 690 is a high-chromium nickel alloy having very low corrosion rates in many

corrosive aqueous media and high-temperature atmospheres In various types of high-temperature water, alloy 690 also displays low corrosion rates and excellent resistance to stress-corrosion cracking—desirable attributes for nuclear steam-generator tubing In addition, the alloy's resistance

to sulfur-containing gases makes it a useful material for such applications as coal-gasification units, burners and ducts for processing sulfuric acid, furnaces for petrochemical processing, and recuperators and incinerators

Inconel alloy 706 is a precipitation-hardenable alloy with characteristics similar to alloy 718,

except that alloy 706 has considerably improved machinability It also has good resistance to oxidation and corrosion over a broad range of temperatures and environments Like alloy 718, alloy 706 has excellent resistance to postweld strain-age cracking Typical applications are gas-turbine components and other parts that must have high strength combined with good machinability and weldability

Inconel alloy 718 is an age-hardenable high-strength alloy suitable for service at temperatures

from -2530C (-4230F) to 7040C (130O0F) The fatigue strength of alloy 718 is high, and the alloy exhibits high stress-rupture strength up to 7040C (130O0F) as well as oxidation resistance up to 9820C (180O0F) It also offers good corrosion resistance to a wide variety of environments The outstanding characteristic of alloy 718 is its slow response to age hardening The slow response enables the material to be welded and annealed with no spontaneous hardening unless it is cooled slowly Alloy

718 can also be repair-welded in the fully aged condition Typical applications are jet engine com-ponents, pump bodies and parts, rocket motors and thrust reversers, and spacecraft

Inconel alloy X-750 is an age-hardenable nickel-chromium-iron alloy used for its corrosion and

oxidation resistance and high creep-rupture strength up to 8160C (150O0F) The alloy is made age-hardenable by the addition of aluminum, columbium, and titanium, which combine with nickel, during

r Stainless steels j

Add Fe

50 Cr-50 Ni AllovGOl ! ! I Alloys Alloy Alloy bUi j j 825 Q

Add Cr for I Add Mo1 Cu for

resistance to Add Cr, Al for resistance to chlorides,

fuel ash resistance reducing acids

\ to oxidation /

I Alloy 690 I i /

MT"^ Alloys 800, 80OH, 802 Add Cr, lower C for /

resistance to Add Fe for economy and Cr for oxidizing acids carburization, oxidation and S.C.C /resistance

Add Mo1 Cr for Add Cr got I

All°ys resistance to ™$( high-temperature

r6^- ^ chlorides, acids, Nl iscr 8Fe -«-strength resistance- ^ckel

C-276, and high-temperature Nl ibLr yhe to oxidizing 20°

C~4> X environments I | media 1

strengthening / ^ ^

/ Add Mo for resistance to / resistance to reducing acids,

, f reducing acids, seawater

halogens i

Alloy /

Add Co, Mo, B, Zr, W, Cb /

/ Alloys B, B-2 Add ^5,

Superalloys I I

Cupronickels

Fig 5.1 Some compositional modifications of nickel and its alloys to produce

special properties.

proper heat treatment, to form the intermetallic compound Ni3(Al, Ti) Alloy X-750, originally de-veloped for gas turbines and jet engines, has been adopted for a wide variety of other uses because

of its favorable combination of properties Excellent relaxation resistance makes alloy X-750 suitable for springs operating at temperatures up to about 6490C (120O0F) The material also exhibits good strength and ductility at temperatures as low as -2530C (-4230F) Alloy X-750 also exhibits high resistance to chloride-ion stress-corrosion cracking even in the fully age-hardened condition Typical applications are gas-turbine parts (aviation and industrial), springs (steam service), nuclear reactors, bolts, vacuum envelopes, heat-treating fixtures, extrusion dies, aircraft sheet, bellows, and forming tools

Nickel-lron-Chromium Alloys

This series of alloys typically contains 30-45% Ni and is used in elevated- or high-temperature environments where resistance to oxidation or corrosion is required

Incoloy alloy 800 is a widely used material of construction for equipment that must resist

cor-rosion, have high strength, or resist oxidation and carburization The chromium in the alloy imparts resistance to high-temperature oxidation and general corrosion Nickel maintains an austenitic struc-ture so that the alloy remains ductile after elevated-temperastruc-ture exposure The nickel content also contributes resistance to scaling, general corrosion, and stress-corrosion cracking Typical applications are heat-treating equipment and heat exchangers in the chemical, petrochemical, and nuclear indus-tries, especially where resistance to stress-corrosion cracking is required Considerable quantities are used for sheathing on electric heating elements

Incoloy alloy 80OH is a version of Incoloy alloy 800 having significantly higher creep and rupture

strength The two alloys have the same chemical composition with the exception that the carbon content of alloy 80OH is restricted to the upper portion of the standard range for alloy 800 In addition

to a controlled carbon content, alloy 80OH receives an annealing treatment that produces a coarse grain size—an ASTM number of 5 or coarser The annealing treatment and carbon content are responsible for the alloy's greater creep and rupture strength

Alloy 80OH is useful for many applications involving long-term exposure to elevated temperatures

or corrosive atmospheres In chemical and petrochemical processing, the alloy is used in steam/ hydrocarbon reforming for catalyst tubing, convection tubing, pigtails, outlet manifolds, quenching-system piping, and transfer piping; in ethylene production for both convection and cracking tubes;

in oxo-alcohol production for tubing in hydrogenation heaters; in hydrodealkylation units for heater tubing; and in production of vinyl chloride monomer for cracking tubes, return bends, and inlet and outlet flanges

Industrial heating is another area of wide usage for alloy 80OH In various types of heat-treating furnaces, the alloy is used for radiant tubes, muffles, retorts, and assorted furnace fixtures Alloy 80OH is also used in power generation for steam superheater tubing and high-temperature heat ex-changers in gas-cooled nuclear reactors

Incoloy alloy 825 was developed for use in aggressively corrosive environments The nickel

content of the alloy is sufficient to make it resistant to chloride-ion stress-corrosion cracking, and, with molybdenum and copper, alloy 825 has resistance to reducing acids Chromium confers resis-tance to oxidizing chemicals The alloy also resists pitting and intergranular attack when heated in the critical sensitization temperature range Alloy 825 offers exceptional resistance to corrosion by sulfuric acid solutions, phosphoric acid solutions, and seawater Typical applications are phosphoric acid evaporators, pickling-tank heaters, pickling hooks and equipment, chemical-process equipment, spent nuclear fuel element recovery, propeller shafts, tank trucks, and oil-country cold-worked tubulars

Incoloy alloy 925 was developed for severe conditions found in corrosive wells containing H2S,

CO2, and brine at high pressures Alloy 925 is a weldable, age-hardenable alloy having corrosion and stress-corrosion resistance similar to Incoloy alloy 825 It is recommended for applications where alloy 825 does not have adequate yield or tensile strength for service in the production of oil and gas, such as valve bodies, hanger bars, flow lines, casing, and other tools and equipment

Pyromet 860 and Refractaloy 26 are high-temperature precipitation-hardenable alloys with lower

nickel content than Inconel alloy X-750 but with additions of cobalt and molybdenum The precip-itation-hardening elements are the same except the Al/Ti ratio is reversed with titanium content being greater than aluminum Typical applications of both alloys are critical components of gas turbines, bolts, and structural members.8

Nickel-Iron

The nickel-iron alloys listed in Table 5.1 as a group have a low coefficient of expansion that remains virtually constant to a temperature below the Curie temperature for each alloy A major application

for NiIo alloy 36 is tooling for curing composite airframe components The thermal expansion char-acteristics of NiIo alloy 42 are particularly useful for semiconductor lead frames and glass-sealing

applications

Ni-Span-C alloy 902 and Incoloy alloys 903 and 907 are precipitation-hardenable alloys with

similar thermal expansion characteristics to NiIo alloy 42 but having different constant coefficient of expansion temperature range Alloy 902 is frequently used in precision apparatus where elastic mem-bers must maintain a constant frequency when subjected to temperature fluctuations Alloys 903 and

907 are being used in aircraft jet engines for members requiring high-temperature strengths to 6490C (120O0F) with thermal expansion controlled to maintain low clearance

Nickel-Chromium-Molybdenum Alloys

This group of alloys contains 45-60% Ni and was developed for severe corrosion environments Many of these alloys also have good oxidation resistance and some have useful strength to 10930C (200O0F)

Hastelloy alloy X is a non-age-hardenable nickel-chromium-iron-molybdenum alloy developed

for high-temperature service up to 12040C (220O0F) Typical applications are furnace hardware sub-jected to oxidizing, reducing, and neutral atmospheres; aircraft jet engine tail pipes; and combustion cans and afterburner components.'

Hastelloy alloy C is a mildly age-hardenable alloy similar in composition to alloy X except nearly

all the iron is replaced with molybdenum and nickel It is highly resistant to strongly oxidizing acids, salts, and chlorine It has good high-temperature strength Typical applications are chemical, petro-chemical, and oil refinery equipment; aircraft jet engines; and heat-treating equipment.6'7

Hastelloy alloy C-276 is a modification of Hastelloy alloy C where the carbon and silicon content

is reduced to very low levels to diminish carbide precipitation in the heat-affected zone of weldments Alloy C-276 is non-age-hardenable and is used in the solution-treated condition No postwelding heat treatment is necessary for chemical-process equipment Typical applications are chemical- and petro-chemical-process equipment, aircraft jet engines, and deep sour gas wells.6'7

Hastelloy alloy G is a non-age-hardenable alloy similar to the composition of alloy X but with

2% copper and 2% columbium and lower carbon content Alloy G is resistant to pitting and stress-corrosion cracking Typical applications are paper and pulp equipment, phosphate fertilizer, and syn-thetic fiber processing.6'7

Inconel alloy 617 is a solid-solution-strengthened alloy containing cobalt that has an exceptional

combination of high-temperature strength and oxidation resistance which makes alloy 617 a useful material for gas-turbine aircraft engines and other applications involving exposure to extreme tem-peratures, such as, steam generator tubing and pressure vessels for advanced high-temperature gas-cooled nuclear reactors

Inconel alloy 625, like alloy 617, is a solid-solution-strengthened alloy but containing columbium

instead of cobalt This combination of elements is responsible for superior resistance to a wide range

of corrosive environments of unusual severity as well as to high-temperature effects such as oxidation and carburization The properties of alloy 625 that make it attractive for seawater applications are freedom from pitting and crevice corrosion, high corrosion fatigue strength, high tensile strength, and resistance to chloride-ion stress-corrosion cracking Typical applications are wire rope for moor-ing cables; propeller blades; submarine propeller sleeves and seals; submarine snorkel tubes; aircraft ducting, exhausts, thrust-reverser, and spray bars; and power plant scrubbers, stack liners, and bellows

MAR-M-252, Rene' 41, Rene' 95, and Astroloy are a group of age-hardenable nickel-base alloys

containing 10-15% cobalt designed for highly stressed parts operating at temperatures from 871 to

9820C (1600 to 180O0F) in jet engines MAR-M-252 and Rene' 41 have nearly the same composition but Rene' 41 contains more of the age-hardening elements allowing higher strengths to be obtained Rene' 95, of similar base composition but in addition containing 3.5% columbium and 3.5% tungsten,

is used at temperatures between 371 and 6490C (700 and 120O0F) Its primary use is as disks, shaft retaining rings, and other rotating parts in aircraft engines of various types.6"8

Udimet 500, 520, 600, and 700 and Unitemp 1753 are age-hardenable, nickel-base alloys having

high strength at temperatures up to 9820C (180O0F) All contain a significant amount of cobalt Applications include jet engine gas-turbine blades, combustion chambers, rotor disks, and other high-temperature components.6"8

Waspaloy is an age-hardenable nickel-base alloy developed to have high strength up to 76O0C (140O0F) combined with oxidation resistance to 8710C (160O0F) Applications are jet engine turbine buckets and disks, air frame assemblies, missile systems, and high-temperature bolts and fasteners.6"8

Nickel Powder Alloys (Dispersion Strengthened)

These oxide dispersion strengthened (ODS) alloys are produced by a proprietary powder metallurgical process using thoria as the dispersoid The mechanical properties to a large extent are determined by the processing history The preferred thermomechanical processing results in an oriented texture with grain aspect ratios of about 3:1 to 6:1

TD-nickel and TD-NiCr are dispersion-hardened nickel alloys developing useful strengths up to

12040C (220O0F) These alloys are difficult to fusion weld without reducing the high-temperature strength Brazing is used in the manufacture of jet engine hardware Applications are jet engine parts, rocket nozzles, and afterburner liners.6"8

Nickel Powder Alloys (Mechanically Alloyed)

Inconel alloy MA 754 and Inconel alloy MA 6000 are ODS nickel-base alloys produced by mechanical

alloying.910 An yttrium oxide dispersoid imparts high creep-rupture strength up to 11490C (210O0F)

MA 6000 is also age-hardenable, which increases strength at low temperatures up to 76O0C (140O0F) These mechanical alloys like the thoria-strengthened alloys described are difficult to fusion weld without reducing high-temperature strength Useful strength is obtained by brazing MA 754 is being used as aircraft gas-turbine vanes and bands Applications for MA 6000 are aircraft gas turbine buckets and test grips

5.3 CORROSION

It is well recognized that the potential saving is very great by utilizing available and economic practices to improve corrosion prevention and control Not only should the designer consider initial cost of materials, but he or she should also include the cost of maintenance, length of service, downtime cost, and replacement costs This type of cost analysis can frequently show that more highly alloyed, corrosion-resistant materials are more cost effective The National Commission on